1. Field of the Invention
The present invention generally relates to magneto-resistive effect devices, and particularly to a magneto-resistance effect element effectively utilizing a giant magneto-resistive effect (GMR effect) having a what might be called a spin-valve configuration, a magnetic sensor using magneto-resistive effect, a magnetic head using magneto-resistive effect and a magnetic memory.
2. Description of the Related Art
In general, a magnetic sensor comprised of a magneto-resistive effect: element and a magnetic head using such a magnetic sensor as a magnetic sensing portion are widely employed as a transducer to read out a magnetic field of a recorded signal from a magnetic recording medium, for example, at large linear density.
Magneto-resistive effect elements according to the related-art generally make effective use of an anisotropic magneto-resistive effect in which a resistance of a magneto-resistive effect element changes in proportion to a square of a cosine of an angle formed between the magnetization of the element and the direction in which a sense current, which flows through the element, is conducted.
In recent years, magneto-resistive effect elements using a magneto-resistive effect based upon a GMR (giant magneto-resistive) effect, in particular, a spin-valve effect in which a resistance change of an element through which a sense current is flowing is generated due to a spin-dependence of electric conduction electrons between magnetic layers disposed through a nonmagnetic layer and a spin-dependence scattering that occurs at the interfaces of respective layers have become popular increasingly.
Since the magneto-resistive effect element using the magneto-resistive effect based upon this spin-valve effect (hereinafter simply referred to as an “SV type GMR element”) can exhibit a resistance change larger than that of the above-mentioned magneto-resistive effect element using the anisotropic magneto-resistive effect, the SV type GMR element is able to make up a highly-sensitive magnetic sensor and a highly-sensitive magnetic head.
In order to record data on a magnetic recording medium at recording density of up to about 50 gigabytes/inch2, a magnetic head using a magneto-resistive effect element as a magnetic sensing portion may have a configuration which is what might be called a CIP (current in-plane) configuration in which a sense current flows to the plane direction of a thin film. However, when it is requested that data should be recorded on a magnetic recording medium at higher recording density, e.g., recording density of 100 gigabytes/inch2, it is requested that a track width should be reduced to a track width of approximately 0.1 μm. According to the above-mentioned CIP configuration, even when the latest dry process is effectively utilized as a present patterning technique to manufacture magneto-resistive effect element, there is a limitation on forming such magneto-resistive effect element which can realize the above-mentioned high recording density and which can also realize the above-mentioned narrow track width. Furthermore, according to the above-mentioned CIP configuration, since it is necessary that a resistance should be lowered, a cross-sectional area of a current path has to be increased. As a result, there is a limitation on making such a narrow track width.
On the other hand, in the SV type GMR element, there has been proposed a GMR element having a configuration which is what might be called a “CPP (current perpendicular to plane) configuration in which a sense current flows in the direction perpendicular to the film plane.
A TMR (tunnel magneto-resistive) element using a tunnel current has been examined, and in recent years, spin-valve elements and multilayer film type elements have been examined (e.g., see Japanese patent translation No 11-509956, Japanese laid-open patent application No. 2000-30222, Japanese laid-open patent application No. 2000-228004 and The Abstract of the Lectures of the 24th Meeting of The Society for Applied Magnetics of Japan 2000, page 427).
Since the GMR element having the CPP configuration allows the sense current to flow in the direction perpendicular to the film plane as described above, this giant magneto-resistive effect element cannot exhibit a sufficiently high sensitivity when it is applied to the spin-valve type film configuration having the CIP configuration in which a sense current flows in the direction extending along the film plane. The reason for this will be described below. That is, while the giant magneto-resistive effect element having the CIP configuration utilizes a resistance change caused by a spin-dependence scattering that occurs when a sense current flows mainly in the direction parallel to an electric conduction layer in the spin-valve type film configuration and to the interface of the electric conduction layer, when the giant magneto-resistive effect element has the CPP configuration, a sense current flows in the direction perpendicular to the film plane with the result that this effect cannot act effectively.
On the other hand, according to the reports, it is to be understood that the resistance change could be improved in accordance with the increase of the thickness of the free layer in the spin-valve configuration (see the above-mentioned Abstract of the Lectures of The Society for Applied Magnetics of Japan).
However, since a distance in which electric conduction electrons are able to continue spinning is limited, a resistance change cannot be improved sufficiently by increasing the thickness of the free layer.
Furthermore, in order to increase the sensitivity of the magneto-resistive effect element serving as the magnetic head, it is necessary that a product of a saturated magnetization Ms of a free layer and a film thickness t, i.e., a value of Ms×t should be decreased. Accordingly, it is to be appreciated that the above-mentioned method of improving the resistance change by increasing the film thickness of the free layer is not a present essential solution for realizing high recording density, very small recording and reproducing bits and high sensitivity.